The experiments described in this application address the overall question of how proteins and glycoproteins attach to sperm surfaces as sperm proceed through the epididymis. The importance to health of the questions being asked is that as sperm enter the epididymis they are unable to fertilize eggs, but after moving through the epididymis they are. Thus, understanding "maturational" events (such as how molecules from epididymal fluid attach to sperm) will help in the genera understanding of the mechanisms both of fertility and infertility. We have discovered that a approximately 24 kDa antigen on rat sperm plasma membrane, which is added to sperm in the epididymis, is linked to the sperm plasma membrane by way of phosphotidylinositol (PI), a new linkage that has been found in a number of important cell surface molecules. It is proposed in this application to study in detail the linkage approximately 24 kDa has with sperm, to purify approximately 24 kDa and to do amino acid composition and sequence studies. It is also proposed to identify the site of synthesis of precursor(s) approximately 24 kDa and the mechanisms regulating its (their) synthesis (using cDNA and cRNA probes, as well as precursor incorporation) and secretion. The grant will also address the mechanisms of the sequence of binding of approximately 24 kDa to sperm. Finally, it is proposed to search for a physiological role for approximately 24 kDa, particularly related to motility and energy substrate transport.